1. Field of the Invention
The present invention relates to devices for monitoring and adjusting cooling circuit temperatures, and in particular to devices for monitoring and adjusting the temperatures of multiple cooling circuits, as are used in heat-generating production machines, for example injection molding machines.
2. Description of the Prior Art
In the case of an injection molding machine, for example, there are several critical zones in which the temperature must be continuously monitored and maintained within a comparatively narrow range. Among these critical zones are the injection molding die itself, the inlet region of the plastification cylinder, and the hydraulic pressure fluid used in the hydraulic system of the machine. Thus, when for instance the temperature of the injection molding die drops below the empirically determined optimal temperature, the quality of the molded parts suffers and their dimensional accuracy is negatively affected. These dimensional deviations may be the result of residual material stress inside the molded parts, which stress may also reduce the mechanical resistance of the parts. If, on the other hand, the temperature in the critical zone of the injection molding die is above the optimal value, the cycle duration of the machine is markedly longer. This means that valuable time is wasted during each production cycle, the result being a reduction in productive efficiency.
The critical temperature zone in the plastification cylinder of the injection unit is located at the granulate inlet to the plastification screw. If this temperature drops below the optimal value, the plastification output of the plastification cylinder is reduced. A temperature above the optimal value results in material smudging around the granulate intake, and in extreme cases, in jamming at the intake zone.
Lastly, the temperature of the hydraulic pressure medium has to be monitored and maintained at its optimal value, within a comparatively narrow range. This optimal temperature is comprised between approximately 40.degree. and 50.degree. C. If the temperature of the hydraulic oil falls below this range, the pressure medium begins to "knock", thereby reducing the operating efficiency of the machine, while increasing the mechanical stress to which various critical components, e.g. valve components, are subjected. If the hydraulic oil becomes too hot, it tends to reduce the longevity of heat-sensitive sealing elements, such as rubber gaskets and plastic parts, for example.
Other critical temperature zones may be encountered in an injection molding machine at places where considerable heat is generated from mechanical friction.
From prior art in this field is known a device for visually monitoring the flow speed of a liquid medium: German Published Application (Offenlegungsschrift) No. 1,812,883.
In the case of injection molding machines, for example, it has heretofore not been possible to monitor and maintain within a narrow optimal temperature range the above-mentioned critical temperature zones of the machine with means which are both simple in structure and satisfactory in operation.